Hydraulic load-handling clamp assemblies, of the type normally mountable on lift trucks and other industrial vehicles for manipulating and transporting loads, often have a pair of transversely openable and closable clamp arms powered by one or more linear or rotary hydraulic actuators for selectively gripping and releasing loads. Such hydraulic clamp assemblies also commonly have a selectable hydraulic side-shifting capability which can move the clamp arms transversely in unison in either of two opposite directions while clamping a load. In some of such clamp assemblies, the same hydraulic actuator(s) which perform the load-clamping function also selectively perform the side-shifting function, thereby advantageously minimizing the size and weight of the assembly. Such systems are referred to herein as “integral” load clamping and side-shifting units. Conversely, in “non-integral” systems, the clamp assembly's load-clamping hydraulic actuator(s) are movably carried by a separate side-shifting assembly having its own separate side-shifting hydraulic actuator(s).
A longstanding problem has existed with respect to both the foregoing integral and non-integral types of units, in that the above-described load-clamping function requires load clamping forces applied by both clamp arms to the load in respective opposite directions, while at the same time the side-shifting function requires side-shifting forces applied by both clamp arms in the same direction. The result is that the bidirectional clamping force is automatically diminished by the simultaneous unidirectional side-shifting force, thereby enabling a clamped load to slip and fall from the clamp during side-shifting if the side-shifting force is too great relative to the clamping force. The most problematic situation of this type occurs when limited hydraulic clamping force is already being applied to grip a fragile load to avoid overclamping damage to the load, at the same time that the hydraulic side-shifting force is not being sufficiently limited due to the damp operator's desire for rapid side-shifting.
The foregoing summary will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.